The present invention relates to a device for changing compression of a reciprocating piston internal combustion engine comprising a crankshaft that is supported within the motor housing, a connecting rod supported at a crank of the crankshaft, a piston reciprocating within a cylinder of the motor housing and supported at the connecting rod, and an eccentric bushing which with its cylindrical inner surface is supported at the crank and with an eccentric outer cylindrical surface resting at the connecting rod so that by rotation of the bushing relative to the connecting rod the effective length of the connecting rod can be changed.
An adaptation of the compression to the respective operating conditions of an internal combustion engine, especially in regard to load conditions under which the internal combustion engine operates, has been desired for a long time. For example, when during minimal load the compression is increased and at full load is reduced, a considerable fuel reduction and a greater possible output distribution range can be achieved.
From German patent 42 26 361 a device for changing the compression of a reciprocating piston internal combustion engine of the aforementioned kind is known in which within the connecting rod a crank pin bearing is provided that is hydraulically adjustable by an eccentric. The eccentric is an eccentric disc embodied as a circular or rotary piston having at least one radially projecting piston which is hydraulically displaceable in a radial extension of the eccentric disc bearing. The hydraulic supply for actuating the piston is realized by an oil supply from the crank case which requires a comparatively complicated design. In a further embodiment of the known device, the hydraulic piston can be loaded on both sides with hydraulic medium whereby the pressure chamber supporting the pushing force of the connecting rod during the intake stroke of the piston is opened for refilling with pressure medium by minimal displacement of the hydraulic piston and during the compression stroke is opened for pressure medium exhaust by the hydraulic piston. During the working stroke the pressure chamber is closed. An adjustment of the opening parameters is such that for the desired degree of compression pressure the hydraulic medium exhaust is identical to the pressure medium refill. In this manner a predetermined, optimal compression is to be maintained. The control of the pressure chambers is however relatively complicated. Also, the eccentric disc is rotated such that the crank pin bearing is arranged non-centrally relative to the connecting rod which in many respects results in unfavorable load distribution.
From German patent application 38 18 357 a device for changing the compression of a reciprocating piston internal combustion engine is disclosed in which the eye of the connecting rod is supported by an eccentric sleeve at the piston bolt. The eccentric sleeve or bushing comprises at its outer circumferential surface a plurality of cutouts which can be engaged by lungers, arranged within the connecting rod and movable by a high hydraulic medium, so that the rotary position of the eccentric bushing can be locked. The oil supply and the valves required for the control are of a relatively complicated design. In addition, constructive space is required within the piston.
It is therefore an object of the present invention to provide a device for changing the compression of a reciprocating piston internal combustion engine which provides a high degree of functional safety but has a simple design.